Method for controlling an internal combustion engine

ABSTRACT

An internal combustion engine has a camshaft whose phase can be adjusted with respect to a crankshaft by means of a setting mechanism. Also provided are a crankshaft sensor which senses the crankshaft angle and a camshaft sensor which senses the camshaft angle. The method comprises the following steps: A reference value for the phase is adapted in a predefined position of the setting mechanism when a predefined condition is satisfied. A measurement value for the phase is determined depending on the sensed crankshaft angle and camshaft angle. A corrected measurement value for the phase is determined depending on the reference value and the measurement value for the phase. A control signal for controlling the internal combustion engine is determined depending on the corrected measurement value.

CROSS REFERENCE TO RELATED APPLICATION

This application is the U.S. National Stage of International ApplicationNo. PCT/EP2004/000266, filed Jan. 15, 2004 and claims the benefitthereof. The International Application claims the benefits of GermanPatent application No. 10307307.8 DE filed Feb. 20, 2003, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The invention relates to a method for controlling an internal combustionengine having a camshaft whose phase can be adjusted with respect to acrankshaft by means of a setting mechanism.

BACKGROUND OF THE INVENTION

A method for controlling an internal combustion engine having a camshaftwhose phase can be adjusted with respect to a crankshaft by means of asetting mechanism is known from DE 101 08 055 C1. The setting mechanismdisclosed in that publication is a hydraulic system by means of whichthe phase relationship between the crankshaft and the camshaft can beadjusted. Setting mechanisms of this type are widely used in moderninternal combustion engines and are used on the one hand to improveperformance and on the other hand to reduce emissions in the internalcombustion engine.

With regard to the method known from DE 101 08 055 C1, near to the timewhen the internal combustion engine starts up a measurement value isdetermined for the phase between the crankshaft and the camshaftdepending on sensed camshaft and crankshaft angles. A predefinedinitialization value is read in from a memory. The initialization valueof the phase relationship is the value of the phase which the camshaftand the crankshaft have with respect to one another when all themechanical components are arranged in the predefined manner with respectto one another. Such initialization values are typically fixed andpredefined by the manufacturer of the internal combustion engine for allinternal combustion engines of a series and stored in the controlfacilities provided for this purpose.

A correction value for the phase is then determined near to the timewhen the internal combustion engine starts up, depending on thedifference between the initialization value and the measurement valuefor the phase. During the further operation of the internal combustionengine, the current phase in each case is then determined from the sumof the measurement value and the correction value. With regard to theknown method, it is assumed that errors in the measurement value for thephase can essentially be attributed to the tolerances for the crankshaftsensor and the camshaft sensor. It has become apparent however that inspite of these corrections the desired low-emission operation of theinternal combustion engine is not always guaranteed.

SUMMARY OF THE INVENTION

The object of the invention is to set down a method for controlling aninternal combustion engine having a camshaft whose phase can be adjustedwith respect to a crankshaft by means of a setting mechanism, whichensures low-emission operation.

This object is achieved by the features of the independent claim.Advantageous embodiments of the invention are set down in the subclaims.

The invention is based on the knowledge that during operation of theinternal combustion engine when there is a rigid assignment between theinitialization value and a reference value an error occurs duringoperation of the internal combustion engine when generating the settingsignal. In this situation, it has surprisingly become apparent thaterrors can be attributed not only to tolerances and drift phenomenarelating to the crankshaft sensor and the camshaft sensor but also tochanges or wear in the area of the setting mechanisms or also in otherelements which are used for coupling purposes between the crankshaft andthe camshaft, such as corresponding gear wheel or a chain. Considerablechanges can thus occur in the actual phase relationship between thecrankshaft and the camshaft which for example in comparison with theinitialization value for the phase relationship can come to up to +−15°crankshaft and thus significantly influence the mass flow feed into thecylinders of the internal combustion engine. On the basis of thisknowledge, in accordance with the object of the independent claim areference value for the phase is adapted in a predefined position of thesetting mechanism when a predefined condition is satisfied. Duringfurther operation of the internal combustion engine a correctedmeasurement value for the phase is then determined depending on thereference value and a measurement value for the phase. It is thereforethen simple to ensure that the internal combustion engine is capable oflow-emission operation.

In an advantageous embodiment of the invention the predefined conditionis satisfied when a motor vehicle in which the internal combustionengine can be located has traveled a predefined journey distance sincethe last adaptation and predefined ambient conditions exist. Thisembodiment of the condition is characterized by the fact that it ensuressimple and precise adaptation with a reasonable computational effort.

A further advantageous embodiment of the invention is characterized bythe fact that the ambient conditions exist when the temperature of theinternal combustion engine lies within a predefined range. This has theadvantage that no falsification is incorporated during the adaptation asa result of any temperature drift of the sensors which may possiblyactually occur.

If the adaptation takes place near to the time when the internalcombustion engine starts up, this has the advantage that the settingmechanism is situated in the end position predefined by the mechanicalsetup and a precise adaptation of the reference value is thusguaranteed.

If the adaptation takes place depending on a variable which ischaracteristic of the load on the internal combustion engine, then as aresult a precise adaptation can simply take place since the load on theinternal combustion engine is substantially responsible for changes inthe reference position.

In this situation the method becomes particularly simple if the variablewhich is characteristic of the loading on the internal combustion engineis the journey distance or the method becomes particularly precise ifthis variable is a variable which is characteristic of the full loadacceleration.

It is particularly advantageous if the variable which is characteristicof the loading on the internal combustion engine is a variable which ischaracteristic of an uneven running state. As a result the methodbecomes particularly precise and can go back to a variable which iscalculated in any case for other control or diagnostic functions of theinternal combustion engine in a control unit of the internal combustionengine.

The method also becomes particularly simple if the variable which ischaracteristic of the loading on the internal combustion engine is theperiod of operation of the internal combustion engine.

It is also particularly advantageous if the diagnostics for the internalcombustion engine are carried out depending on the adapted referencevalue or a value which determines the adaptation, then precisediagnostics are also enabled at the same time using a value which iscalculated in any case by the method.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in thefollowing with reference to the schematic drawings, in which;

FIG. 1 shows an internal combustion engine having a control unit inwhich the method for controlling the internal combustion engine isprocessed,

FIG. 2 shows a setting mechanism assigned to the internal combustionengine according to FIG. 1 for adjusting the phase between a camshaftand a crankshaft,

FIG. 3 shows valve stroke progression curves for the gas-reversingvalves, plotted against the crankshaft angle,

FIG. 4 shows a flowchart of a program for one part of the method forcontrolling the internal combustion engine,

FIGS. 5, 6 show a flowchart of a program for a further part of themethod for controlling the internal combustion engine,

FIG. 7 shows a program for a method for performing diagnostics on theinternal combustion engine.

Elements having the same design or function bear the same referencecharacters across all the figures.

DETAILED DESCRIPTION OF THE INVENTION

An internal combustion engine (see FIG. 1) comprises an intake tract 1,an engine block 2, a cylinder head 3 and an exhaust tract 4. The intaketract preferably comprises a throttle valve 11, and also a header 12 andan induction manifold 13 which is routed towards a cylinder Z1 by way ofan inlet port into the engine block. The engine block also comprises acrankshaft 21 which is coupled by way of a connecting rod to the pistonof the cylinder Z1.

The cylinder head comprises a valve drive assembly comprising an inletvalve 30, an outlet valve 31 and valve drives 32, 33. In this situation,the drive for the gas inlet valve 30 and for the gas outlet valve 31 ispreferably effected by means of a camshaft 36 (see FIG. 2), or shouldthe occasion arise by means of two camshafts whereby one is assigned tothe gas inlet valve 30 and one to the gas outlet valve 31. The drive forthe gas inlet valve 30 and/or the gas outlet valve 31 preferablycomprises, in addition to the camshaft 36, a setting mechanism 37 whichis coupled on the one side with the camshaft 36 and on the other sidewith the crankshaft 21, for example by way of toothed wheels which arecoupled to one another by way of a chain. The phase between thecrankshaft 21 and the camshaft 36 can be adjusted by means of thesetting mechanism. This is done in the present exemplary embodiment byincreasing the pressure in the high-pressure chambers 38 of the settingmechanism 37 or by reducing the corresponding pressure, depending on thedirection in which the adjustment is to be made. The possible range ofadjustment is indicated in FIG. 2 by the arrow 39.

The valve lift curves 46, 47 represented as dashed lines (FIG. 3) forthe inlet valves 30 and outlet valves 31 illustrate the situation inwhich they match the initialization value. During operation of theinternal combustion engine these valve lift curves can however changetowards the valve lift curves 45 and 48. This has the consequence thatwith the valve drive in its end position the valve overlap between thegas inlet and gas outlet valves can then be different to the originalvalve overlap and their phases or their position can also be displacedwith reference to the crankshaft angle.

Trials have shown that a displacement of up to +/−15° crankshaft canresult in this situation. Such displacements then result in changedgas-reversing operations and changed combustion operations, as a resultof which without the method described in the following it is then nolonger possible to ensure that the desired torque is set on the one handand that low-emission operation of the internal combustion engine isguaranteed on the other hand.

The cylinder head 3 (FIG. 1) additionally comprises an injection valve34 and a spark plug 35. Alternatively, the injection valve can also belocated in the intake tract.

A catalytic converter 40 is located in the exhaust tract. In addition, acontrol unit 6 is provided which has sensors assigned to it that sensedifferent measured variables and determine the measurement value of themeasured variable in each case. Depending on at least one of themeasured variables, the control unit 6 determines regulating variableswhich are then converted into one or more control signals forcontrolling the control elements by means of appropriate actuators.

The sensors are a pedal position sensor 71 which senses the position ofan accelerator pedal, an air mass meter 14 which senses an air mass flowupstream of the throttle valve 11, a temperature sensor 15 which sensesthe intake air temperature, a pressure sensor 16 which senses theinduction manifold pressure, a crankshaft angle sensor 22 which senses acrankshaft angle CAM, a further temperature sensor 23 which senses acoolant temperature, a camshaft sensor 36 which senses the camshaftangle CRK and an oxygen probe 41 which senses the residual oxygencontent of the exhaust in the exhaust tract 4 and assigns an air ratioto the latter. Depending on the embodiment of the invention, any desiredsubset of the aforementioned sensors, or also additional sensors, can bepresent.

The control elements are for example the throttle valve 11, the gasinlet and gas outlet valves 30, 31, the injection valve 34, and thespark plug 35. They are driven by means of electrical,electromechanical, hydraulic, mechanical piezo or further actuatorsknown to the person skilled in the art. The actuators and controlelements are referred to in the following as control elements.

In addition to the cylinder Z1 represented in detail, further cylindersZ2 through Z4 are usually present in the internal combustion engine,with which cylinders are then associated corresponding inductionmanifolds, exhaust tracts and control elements.

FIG. 4 shows a flowchart of a program for a first part of the method forcontrolling the internal combustion engine. The program is started in astep S1 and this preferably occurs when the internal combustion enginehas been completely assembled and subjected to a final test, theso-called end-of-line test. It is however also advantageous to start themethod in each situation when mechanical intervention has occurred inrespect of the crankshaft 21, the camshaft 36, the setting mechanism 37or any other parts serving to provide the coupling between thecrankshaft 21 and the camshaft 36. Such a situation exists for examplewhen the chain which serves to couple the crankshaft to the camshaft isreplaced or has been re-tensioned.

In a step S2 a measurement value is calculated for the phase dependingon the measurement values determined by the camshaft sensor 36 a and thecrankshaft angle sensor 22 for the camshaft angle CAM and the crankshaftangle CRK. In this situation, the phase between the camshaft and thecrankshaft is related to degrees crankshaft, the top dead center TDC forthe piston assigned to the cylinder Z1 in each case and the vertex ofthe valve lift VL of the inlet valve 30 or the outlet valve 31respectively. Sensing of the measurement value PH_S for the phase takesplace in step S2 under predefined ambient conditions, preferably at apredefined temperature for the internal combustion engine.

In a step S3 a check is performed as to whether the measurement valuePH_S deviates by more than a first threshold value HYS from theinitialization value PH_INI for the phase. The initialization valuePH_INI is a predefined value for the phase for a plurality of internalcombustion engines employing the same construction, in other words aseries of internal combustion engines for example. The initializationvalue PH_INI for the phase is ideally adopted by all internal combustionengines when the setting mechanism is located at its end stop which isgiven by the base of the arrow 39 in FIG. 2.

If in step S3 the deviation exceeds the threshold value HYS, then anemergency mode of operation for the internal combustion engine in whichonly restricted operation of the internal combustion engine is enabledis controlled in a step S4. If the program is started in step S1 duringan end-of-line test, then in step S8 suitable means also enable a signalto be made indicating that the internal combustion engine has not beenproperly assembled or is not in working order.

If the condition in step S3 is not satisfied, however, then in a step S5the measurement value PH_S is assigned to the initialization valuePH_INI. As a result, the phase present with regard to the respectiveindividual internal combustion engine at the end stop of the settingmechanism 37 is then precisely stored. In a step S6 the program is thenterminated.

A program for a further part of the method for controlling the internalcombustion engine is started in a step S7 (see FIG. 5).

In a step S8, a measurement value PH_S for the phase is determineddepending on the sensed crankshaft angles CRK and camshaft angles CAM.In a step S9, a check is performed as to whether an update condition UPDis satisfied. In this situation, a check is preferably performed as towhether the internal combustion engine was started at a point close intime, in other words whether it is still running within the initialrotations of the crankshaft. A check is also performed as to whether aminimum number of driven kilometers has been reached since the lastadaptation of a reference value PH_AD. Finally, a further check isperformed as to whether given ambient conditions, such as preferably apredefined temperature for the internal combustion engine, are met. Inthis situation, the temperature of the internal combustion engine ispreferably determined depending on the sensed coolant temperature.

If the conditions for step S9 are satisfied, then an adaptation value ADis determined in a step S10. The n enclosed in square brackets signifiesin each case that the assigned value for the current calculation cycleis valid as a new value whereas n−1 signifies that the correspondingvalue in the last calculation cycle was the current value.

The adaptation value is determined in step S10 depending on theadaptation value from the last calculation cycle, and/or a journeydistance DIST and/or a number of full-load accelerations LJ and/or aperiod of operation LT. It can also be determined additionally orexclusively depending on a variable which is characteristic of an unevenrunning state of the internal combustion engine or another variablewhich is characteristic of the loading of the internal combustion enginethrough its period of operation. In a step S11, a reference value PH_ADfor the phase of the crankshaft and the camshaft in the end position ofthe setting mechanism 37 is then determined from the sum of theinitialization value and the current adaptation value AD.

In a step S12, a correction value PH_COR is then determined depending onthe reference value PH_AD and the measurement value PH_S for the phase.Simple and additional compensation is then carried out through thiscorrection value PH_COR for temperature and other sensor errors. StepS12 is also processed if the conditions for step S9 are not satisfied.

Concrete embodiments of the determination of the adaptation value AD instep S10 are represented in steps S13 through S16. Thus, the adaptationvalue is determined for example by means of the formula specified instep S13, whereby Min represents a minimum choice from the two termsseparated by commas. The second term of the minimum choice is thedifference between two values which are determined depending on thejourney distance at the current calculation time point and at thepreceding calculation time point and thus represent a maximum change inthe adaptation value AD between two successive adaptations. In thissituation, these values are preferably determined by means ofappropriate driving trials and/or appropriate modeling and arepreferably placed in a characteristic field. This procedure serves toensure in a simple manner that the change in the adaptation value AD instep S13 is limited in terms of scale to a maximum change which ispredefined by a modeling process.

The procedure according to step S14 with regard to determining theadaptation value AD differs from that of step S13 in that the secondterm of the minimum choice is a value which is determined depending onthe difference between the current journey distance DIST and the journeydistance DIST present in the last cycle of step S14. The value alsorepresents a model value, whereby in contrast to step S13 it is not theabsolute journey distances which are decisive here but only the relativejourney distances are taken into consideration. In this case too thecalculation of the value is preferably carried out using acharacteristic field.

In steps S15 and S16, the calculation of the adaptation value takesplace by means of a PT1 filtering process. To this end, to theadaptation value determined in the last cycle of step S15 is added aterm which contains a weighting value that is dependent on thedifference between the journey distance DIST at the current calculationtime point and the journey distance during the last calculation cycle ofstep S15. This weighting value is multiplied by the difference betweenthe deviation of the current measurement value PH_S and initializationvalue PH_INI and the adaptation value during the preceding calculationcycle of step S15. In this situation, the weighting factor is preferablydetermined from a characteristic field, stored in the control unit 6,which has been determined through driving trials or on the engine testbed.

Step S16 is distinguished from step S15 by the fact that the weightingfactor is additionally or alternatively determined depending on avariable which is characteristic of the full-load accelerations, inother words the number of these for example. The procedures described insteps S13 through S16 for determining the adaptation value have theadvantage in each case that the respective variables which are relevantthere have an influence on the change in the reference position and thuscontribute to an exact and precise adaptation.

In a step S17 (see FIG. 6), which follows step S12, the program enters await state until a predefined period of time has lapsed or until thecrankshaft has advanced by a predefined angle. In this state, theprogram is preferably interrupted and the computing power of the controlunit 6 is made available to other programs.

In a step S18, a measurement value PH_S for the phase is then determineddepending on the camshaft angle CAM and the crankshaft angle CRK. In astep S19, a corrected measurement value PH_AKT is then determined fromthe sum of the measurement value PH_S and of the correction valuePH_COR.

In a step S20, a control signal SG for controlling the internalcombustion engine is then determined, depending on the correctedmeasurement value PH_AKT. This is done for example by means of aso-called induction manifold model which uses appropriate observerequations to determine an estimated value for the air mass metered intothe cylinder Z1, depending on the corrected measurement value PH_AKT forthe phase between the crankshaft 21 and the camshaft 36 and on furthermeasured variables such as the sensed air mass flow, the throttle valvedegree of opening, the temperature of the intake air and where necessarythe sensed induction manifold pressure. Depending on the estimated valuefor the air mass metered into the cylinder Z1, a desired fuel mass isthen determined and the injection valve 34 is then controlled by meansof an appropriate control signal. In a step S21, a check is thenperformed as to whether a termination condition for the program issatisfied. This can for example consist in the fact that the internalcombustion engine is stopped. If the condition for step S19 issatisfied, then the program is terminated in step S22. Otherwise, theprogram is continued in step S17.

Diagnostics are performed on the internal combustion engine by means ofthe program represented in FIG. 7. The program is started in a step S23.In a step S24, a check is performed as to whether the current adaptationvalue is greater than a further threshold value SWA. The furtherthreshold value SWA is fixed and predefined, and preferably determinedby trials on an engine test bed or in driving trials. If the conditionfor step S24 is satisfied, then the internal combustion engine is placedin an emergency mode of operation in a step S25. If the condition forstep S24 is not satisfied however, then the program is terminated instep S26. As an alternative to step S24, a step S27 can also be providedin which a check is performed as to whether the change in the adaptationvalues from one calculation time point for the adaptation value to thenext calculation time point exceeds a predefined further threshold valueSWB. If this is the case, then the internal combustion engine is placedin the emergency mode of operation in step S25. Otherwise, the programis terminated in step S26.

1. A method for controlling an internal combustion engine having acamshaft, a crankshaft sensor, and a camshaft sensor, comprising:adapting a reference value for a phase of the camshaft in a predefinedposition of a setting mechanism when a predefined condition issatisfied: determining a measurement value for the phase depending on asensed crankshaft angle and a camshaft angle; determining a correctedmeasurement value for the phase depending on the reference value and themeasurement value for the phase; and determining a control signal forcontrolling the internal combustion engine depending on the correctedmeasurement value, wherein the predefined condition is satisfied when amotor vehicle containing the internal combustion engine has traveled apredefined journey distance since the last adaptation and a set ofpredefined ambient conditions are present.
 2. The method according toclaim 1, wherein the set of ambient conditions are present when thetemperature of the internal combustion engine lies within a predefinedrange.
 3. The method according to claim 1 wherein the adaptation takesplace near a time when the internal combustion engine starts up.
 4. TheMethod according to claim 1, wherein the adaptation takes placedepending on a variable that is characteristic of a load on the internalcombustion engine.
 5. A method for controlling an internal combustionengine having a camshaft, a crankshaft sensor, and a camshaft sensor,comprising: adapting a reference value for a phase of the camshaft in apredefined position of a setting mechanism when a predefined conditionis satisfied; determining a measurement value for the phase depending ona sensed crankshaft angle and a camshaft angle; determining a correctedmeasurement value for the phase depending on the reference value and themeasurement value for the phase; and determining a control signal forcontrolling the internal combustion engine depending on the correctedmeasurement value, wherein the adaptation takes place depending on avariable that is characteristic of a load on the internal combustionengine, wherein the variable that is characteristic of the load on theinternal combustion engine is the journey distance.
 6. The methodaccording to claim 4, wherein the variable that is characteristic of theload on the internal combustion engine is a variable that ischaracteristic of the full-load accelerations.
 7. A method forcontrolling an internal combustion engine having a camshaft, acrankshaft sensor, and a camshaft sensor, comprising: adapting areference value for a phase of the camshaft in a predefined position ofa setting mechanism when a predefined condition is satisfied;determining a measurement value for the phase depending on a sensedcrankshaft angle and a camshaft angle; determining a correctedmeasurement value for the phase depending on the reference value and themeasurement value for the phase; and determining a control signal forcontrolling the internal combustion engine depending on the correctedmeasurement value, wherein the adaptation takes place depending on avariable that is characteristic of a load on the internal combustionengine, wherein the variable that is characteristic of loads on theinternal combustion engine is a variable that is characteristic of theuneven running state.
 8. The method according to claim 4, wherein thevariable that is characteristic of the load on the internal combustionengine is the period of operation of the internal combustion engine. 9.A method for controlling an internal combustion engine having acamshaft, a crankshaft sensor, and a camshaft sensor, comprising:adapting a reference value for a phase of the camshaft in a predefinedposition of a setting mechanism when a predefined condition issatisfied; determining a measurement value for the phase depending on asensed crankshaft angle and a camshaft angle; determining a correctedmeasurement value for the phase depending on the reference value and themeasurement value for the phase; and determining a control signal forcontrolling the internal combustion engine depending on the correctedmeasurement value, wherein diagnostics are performed on the internalcombustion engine depending on the adapted reference value or a valuedefining the adaptation.
 10. The method according to claim 5, whereinthe variable that is characteristic of the load on the internalcombustion engine is a variable that is characteristic of the full-loadaccelerations.
 11. The method according to claim 7, wherein the variablethat is characteristic of the load on the internal combustion engine isthe period of operation of the internal combustion engine.